The present invention relates to an encapsulating case or box more particularly intended for hybrid circuits required to operate under high, uniform and hydrostatic pressures.
In the case of low level measurements it is known that amplification electronics must be located as close as possible to the sensor or transducer so as to be able to transmit an amplified signal, which is less disturbed by noise or local interference. Although this is easy to bring about at pressures close to atmospheric pressure it becomes difficult when the pressure of the medium in which the circuit has to operate is high and exceeds, for example, 100 bars.
Thus, the components of hybrid circuits are not normally intended to operate under high pressures and the pellets of integrated circuits or semiconductors, the capacitors and resistors connected to a hybrid circuit substrate break at pressures above a few bars, as does the actual substrate.
Non-limitative examples of circuits operating under high pressures are those submerged at a depth of two or three thousand meters or circuits introduced into pressurized industrial installations, e.g. for measuring flows or pressures.
The generally adopted solution consists of enclosing the electronic circuit in a metal case, which is often round or cylindrical, intended to resist the external pressure. One example is constituted by a "glove finger" which penetrates an industrial installation, but which is not applicable to a circuit submerged under several thousand meters of water. In this case the connection by cable requires the metal case to be provided with so-called "glass/metal" passages, i.e. metal connections sealed in the case by glass beads. However, this type of seal and these passages are very fragile.